5
FN6189.1
April 4, 2006
Application Information
This device provides the ability to reduce the flicker of an
LCD panel by adjustment of the VCOM voltage during
production test and alignment. A 128-step resolution is
provided under digital control, which adjusts the sink current
of the output. The output is connected to an external voltage
divider, so that the device will have the capability to reduce
the voltage on the output by increasing the output sink
current.
The adjustment of the output is provided by the 2 wire I
2
C
serial interface.
Expected Output Voltage
The ISL45041 provides an output sink current which lowers
the voltage on the external voltage divider (VCOM output
voltage). Equation 1 and Equation 2 can be used to calculate
the output current (IOUT) and output voltage (VOUT) values.
NOTE: Where setting is an integer between 1 and 128.
Table 1 gives the calculated value of VOUT for the eval
board using the on board resistors values of: RSET = 24.9k,
R1 = 200k, R2 = 243k, and AVDD = 10V.
R
SET
Resistor
The external R
SET
resistor sets the full-scale sink current
that determines the lowest voltage of the external voltage
divider R
1
and R
2
(Figure 1). The maximum I
SET
current has
to be less than 120
μ
A. The minimum RSET resistor with
AVDD equal to 10V is 4.17k
Ω
(10V/(20*120
μ
A). Typical
applications with AVDD equal to 10V set R
SET
equal to
24.9k
Ω
for a set current equal to 20
μ
A.
Ramp-Up of the VDD Power Supply
It is required that the ramp-up from 10% VDD to 90% VDD
level be achieved in less than or equal to 10 ms to assure
that the EEPROM and Power-on-reset circuits are
synchronized and the correct value is read from the
EEPROM Memory.
I
2
C Timing Diagram
Figure 2 shows the I
2
C timing diagram and expected scope
photos of SCL and SDA when writing all zeros or all ones.
R
SET
FIGURE 1. OUTPUT CONNECTION CIRCUIT EXAMPLE
-
+
ISL45041
SET
OUT
AVDD
R
1
R
2
AVDD
I
SET
IOUT
--------------------
X
)
----------------------------
=
VOUT
+
R1
R2
----------------------
AVDD 1
128
--------------------
X
20 RSET
)
----------------------------
–
=
(EQ. 1)
(EQ. 2)
TABLE 1.
SETTING VALUE
VOUT
1
5.468
10
5.313
20
5.141
30
4.969
40
4.797
50
4.625
60
4.453
70
4.281
80
4.109
90
3.936
100
3.764
110
3.592
128
3.282
ISL45041